As one of the modifications of the CZ method, there is known a hot wall method in which a liquid sealing material such as molten B.sub.2 O.sub.3 is used as a sealing material for sealing the apparatus. In this method, a single crystal is pulled up in a container 1 having a structure shown in FIG. 1 which is filled with vapor of volatile component elements of the single crystal (e.g. As). In FIG. 1 the container 1 is provided with a crucible 2 containing a molten raw material and a pulling shaft 4 which pulls up the single crystal with rotation. To the lower end of the shaft 4, a seed crystal 5 is attached. The container is divided into upper and lower portions at a certain part of a side wall, and liquid sealing materials 8 seal an opening 6 of the container 1 and a gap 7 between the pulling shaft 4 and the container 1. The seed crystal is dipped in a surface of the molten raw material in the crucible 2 and, after wetting, pulls up the single crystal with rotation of the seed crystal 5.
Since the container 1 used in this method is made of Quartz, in case of the production of, for example, a GaAs single crystal, the raw material reacts with quartz as follows: EQU 4Ga (in molten GaAs)+SiO.sub.2 (s).fwdarw.2Ga.sub.2 O (g)+Si (in molten GaAs)
and GaAs is contaminated with Si. Therefore, it is difficult to produce, for example, a single crystal suitable for the production of an undoped semi-insulating substrate by the above conventional method.
It is proposed to use pyrolytic boron nitride (hereinafter referred to as "PBN") in place of quartz as the material of the container 1. Since PBN is, however, expensive and its workability is poor, the shape of the container is limited. Further, since PBN is opaque and inevitably the container itself is opaque, the single crystal contained in the container cannot be optically monitored.
In addition, the vapor of the component elements filling the container is supplied by vaporizing solid elements which are beforehand charged in the container in excess amounts, and the vapor pressure is not controlled during pulling up the single crystal. Therefore, a composition of the single crystal cannot be controlled, so that it is difficult to produce a high quality single crystal containing less impurities and having less inherent and crystal defects.